1. Field of the Invention
The present invention relates to transmission and reception of information in a wireless communication system. More particularly, the present invention relates to a method and apparatus for transmitting and receiving transmit power information in a superposition multiple access system.
2. Description of the Related Art
In a system based on Orthogonal Frequency Division Multiple Access (OFDMA) such as 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE), a User Equipment (UE) requires channel information to demodulate its received data. Therefore, a base station transmits a known signal (e.g., a reference signal and a pilot signal) to the UE using a resource element (e.g., a frequency element) adjacent to a data signal so that the UE may perform channel estimation. Importantly, the UE needs to know a relationship between power (i.e., pilot power) of the pilot signal transmitted for channel estimation and power (i.e., data power) of the data signal, in order to correctly perform data detection.
As compared to that of the OFDMA system, a superposition multiple access system has been developed to increase cell capacity. Within one cell in such a system, a base station simultaneously transmits a signal to two or more UEs using the same frequency resource and each UE detects its desired signal from the received signal. To make it easier for a UE to detect its signal, a modulation scheme may be changed. In such a case however, the modulation order may increase such that backward compatibility with a legacy UE may not be guaranteed. In an alternative technology for ensuring easier signal detection by a UE, a base station may transmit a signal to UEs having different pathlosses with different powers. In that case, each UE may remove signals (i.e., interference) from other UEs, which are received with higher power, before it detects its desired signal. In this situation, the UE needs to have an advanced receiver capable of handling interference, in order to obtain performance gain over the legacy system. In other words, by simultaneously handling its desired signal and interference signals using the advanced receiver, the UE may eliminate the influence of the interference and demodulate the overlapping desired signal.
In order to remove the signals from other UEs or perform joint detection with other UEs, the UE needs to obtain power information of the other UEs. However, the conventional communication systems do not offer any means for transferring power information of other UEs.
Furthermore, in the case of joint detection, a desired signal and an interference signal are received at one UE, experiencing the same channel, so the two different signals may have the same estimated channel. In this case, the UE may not exactly distinguish between the two different signals, causing deterioration of the performance of the joint detection.
Therefore, a need exists for an apparatus and method for improving reception performance of a UE in a wireless communication system.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.